The present invention relates to a stationary welding device for the longitudinal welding of profiles, having transport elements for the transport of a profile through the welding device, the transport elements being fashioned such that the movement of the profile can be braked at selectable intervals from a constant production speed down to the stoppage of the profile, and can subsequently be accelerated back to the production speed, and having at least one welding head that produces a weld point in order to manufacture a welded seam on the profile running through the welding device (1), with the application of welding energy to the profile being switched off below a threshold transport speed of the profile. The invention also relates to a corresponding method in which a profile that is to be provided with a weld seam is guided through a welding device, a weld point is produced on the profile in the welding device in order to manufacture a welded seam, the profile movement being braked at selectable intervals from a production speed down to a stoppage of the profile, and being subsequently accelerated back to the production speed, and the application of welding energy to the profile being switched off below the threshold transport speed.
Thus, the invention relates to a stationary welding device having transport elements for transporting a profile through the welding device, and having at least one welding head that produces a weld point in order to manufacture a weld seam on the profile moving through the welding device. The profile movement is braked at selectable intervals from an essentially constant production speed down to a stoppage of the profile, and is subsequently again accelerated to production speed, while the application of welding energy to the profile is switched off below a threshold transport speed of the profile. The method for longitudinal welding of profiles, on which the present invention is also based, corresponds in its features to the function of the described device.
Such devices and methods are typically used in the context of profiling installations in which metal strips are shaped in steps to form profiles or tubes while passing through a multiplicity of roll form tools. The welding station, which is typically subsequent to the tools in the production line, then for example makes it possible to weld together overlapping or abutting regions of the profile or of the tube, or also to weld two or more different profiles with one another.
For a finished product, or a product ready for further processing, the profiles or tubes must be cut into lengths at the end of the production line. Here, in continuously operating production lines traveling cutting machines are used that must be accelerated to the transport speed of the finished profile for the cutting into lengths, so that after the cutting they must naturally be braked and brought back to their initial position.
For such traveling cutting machines, a large construction and maintenance expense is required in order to enable the cuts to be made with the required precision and speed. For this reason, profiling installations having welding devices of the type named above have been developed in which the transport of the welded profile is stopped at selectable intervals, and is subsequently started again. This makes it possible to use a conventional, stationary cutting device for the cutting into pieces of the finished profiles; an expensive traveling cutting machine is thus not required.
However, this results in difficulties in the welding device. The braking of the production speed to the point at which the profile is at a standstill, as well as the subsequent acceleration of the profile to the production speed, each require a certain amount of time and thus a determinate transport distance. The quantity of welding energy that is brought into the profile material at the welding point naturally increases as the welding energy remains constant and the transport speed becomes slower. It is true that this can be compensated for the most part by a reduction of the welding energy, but this can be carried out only up to a threshold transport speed, which depends on the welding technology, below which the welding energy must be completely switched off in order to avoid local destruction of the material.
As a result, in a stationary welding device of the type named above, there remains a gap in the weld seam in the area of the location situated at the welding point during the stoppage of the profile. This gap becomes greater as the production speed is selected higher, and it also depends on how far downward the welding energy can be reduced. To the extent that such a gap in the weld seam is a disturbance in the finished product, it must be removed afterwards; a cutting out of the corresponding point by the stationary cutting machine present in the installation is out of the question, because two cuts are then required for each stop in the production, but each such cut requires two production stops. Thus, up to now the only possibility has been either to use a traveling cutting machine, or else to cut off the scrap separately.